The present invention relates to an oxygen separator, and more particularly, to such a device for separating oxygen from a first gas having a relatively high oxygen partial pressure into a vacuum or a second gas having a relatively low oxygen partial pressure.
Oxygen sensing devices are generally well known. One common type of presently known sensing device functions by monitoring the EMF developed across an oxygen ion conductor which is exposed to gases having different partial pressures of oxygen.
Oxygen tends to move from a gas containing a high concentration of oxygen to one of lower concentration. If the two gases are separated from each other by an oxygen ion conductor, the oxygen molecules will dissociate on one surface of the conductor and absorb electrons to form oxygen ions. These ions can then diffuse through the ionic conductor, leaving the entry surface with a deficiency of electrons. On the exit or low oxygen concentration side of the conductor, oxygen ions leaving the material must give up electrons to form molecular oxygen, leaving the exit surface with an excess of electrons. Thus, an electrical potential difference, or EMF, is set up between the two surfaces of the ion conductor. The greater the difference in oxygen content of the two gases, the greater will be the tendency of oxygen to diffuse through the conductor, and the greater will be potential difference between the entry and exit surfaces.
The EMF generated by the difference in partial pressures may be calculated by the Nernst relation: EQU EMF=t.sub.i (RT/nF) ln (P.sub.O.sbsb.2 /P'.sub.O.sbsb.2), (1)
where t.sub.i is the ionic transference number, R is the gas constant, T is the absolute temperature, n is the number of electrons involved in the electrode reaction, F is the Farady constant, and P.sub.O.sbsb.2 and P'.sub.O.sbsb.2 are the oxygen partial pressures in the first and second gases, respectively. In the present case, the electrode reaction is O.sub.2 +4e.fwdarw.20.sup.-2, and thus n=4.
The basic principles underlying operation of an oxygen separator stem from the same principles responsible for the functioning of the oxygen sensor, and demonstrate the reciprocity principle of physics. If an oxygen ion conducting material separates two gases with different oxygen partial pressures P.sub.O.sbsb.2 and P'.sub.O.sbsb.2, then a voltage signal will appear across the material due to the diffusion of oxygen ions thereacross. The ions diffuse through the material to equalize the partial pressures, and a basic oxygen sensor is the result. However, if a voltage is applied to the oxygen ion conducting material, and if P.sub.O.sbsb.2 =P'.sub.O.sbsb.2, the oxygen ions will be forced to flow across the material such that P.sub.O.sbsb.2 .noteq.P'.sub.O.sbsb.2. Thus, one gas will become richer in oxygen than the other, resulting in a basic oxygen separator.
As an alternative way of viewing the operation of an oxygen separator, consider an oxygen sensor in which a certain voltage signal V is generated by two gases in which P.sub.O.sbsb.2 .noteq.P'.sub.O.sbsb.2. Now, if a reverse voltage -V is applied to the material, the flow of oxygen ions through the material will be completely stopped. Increasing the magnitude of the negative voltage will then cause oxygen ions to flow in a reverse direction.
Consequently, an oxygen separator can be formed by operating an oxygen sensor in reverse. What is needed, therefore, is a physical structure for such a separator that can provide a practical application of these principles.